Thermal desorption preconcentrator adapted for spectroscopic gas analysis

Abstract

Improved gas sample preprocessing is provided for scanning optical spectroscopic analysis instruments by tailoring characteristic gas handling times to the scan time Ts of the analysis instrument. In particular, for sample preconcentration, the desorption duration Td of the sample preconcentrator should be ≥2Ts. For gas chromatography, the elution duration Te of relevant eluted species should be ≥2Ts. This advantageously avoids having significant changes in the gas sample within the analysis instrument as a scan is being performed.

The invention claimed is: 
     
       1. Apparatus for performing gas analysis, the apparatus comprising:
 a gas analysis instrument based on optical absorption spectroscopy, wherein the gas analysis instrument performs a spectral scan in a scan time T s ; 
 a sample preconcentrator having an adsorption mode and a desorption mode; 
 a controller configured to at least switch between the adsorption mode and desorption mode of the sample preconcentrator; 
 wherein the adsorption mode includes receiving an input gas sample and adsorbing one or more constituents of the input gas sample to collect one or more adsorbed species; 
 wherein the desorption mode includes heating the sample preconcentrator to release at least some of the one or more adsorbed species to provide a preprocessed gas sample; 
 wherein the preprocessed gas sample is provided to the gas analysis instrument in a desorption time T d ; 
 wherein T d  is at least 2T s . 
 
     
     
       2. The apparatus of  claim 1 , wherein the desorption time T d  is controlled by controlling a temperature ramp rate of the desorption mode. 
     
     
       3. The apparatus of  claim 1 , wherein the apparatus is configured to provide enhanced concentration of an analyte species to the gas analysis instrument with the sample preconcentrator. 
     
     
       4. The apparatus of  claim 1 , wherein the apparatus is configured to reduce concentrations of one or more interfering gas species provided to the gas analysis instrument using the sample preconcentrator. 
     
     
       5. The apparatus of  claim 1 , wherein the gas analysis instrument is based on a spectroscopy selected from the group consisting of: cavity enhanced absorption spectroscopy, optical-feedback cavity enhanced absorption spectroscopy, cavity ring-down spectroscopy, tunable diode laser absorption spectroscopy, integrated cavity output spectroscopy, and off-axis integrated cavity output spectroscopy. 
     
     
       6. The apparatus of  claim 1 , wherein the sample preconcentrator includes an adsorption/desorption medium selected from the group consisting of: porous polymers, graphitized carbons and carbon molecular sieves. 
     
     
       7. The apparatus of  claim 1 , wherein the adsorption mode includes cooling part or all of the sample preconcentrator to enhance adsorption of the one or more adsorbed species. 
     
     
       8. The apparatus of  claim 1 , wherein the apparatus is configured to measure input sample gas during the adsorption mode with the gas analysis instrument. 
     
     
       9. The apparatus of  claim 1 , further comprising one or more additional gas detectors configured to receive gas from the sample preconcentrator. 
     
     
       10. The apparatus of  claim 1 , wherein the apparatus is configured to provide one or more further sample preconditioning operations selected from the group consisting of: ozone removal, humidity removal, and selective removal of one or more interfering species with gas-selective membranes. 
     
     
       11. The apparatus of  claim 1 , further comprising one or more additional sample preconcentrators, wherein the controller is configured to connect an input of the gas analysis instrument to the sample preconcentrator or to any of the one or more additional sample preconcentrators, thereby providing multiplexing. 
     
     
       12. The apparatus of  claim 1 , wherein the apparatus further includes one or more devices that measure gas flow. 
     
     
       13. The apparatus of  claim 1 , wherein the apparatus further includes one or more fixed gas flow restrictions to provide gas flow control. 
     
     
       14. The apparatus of  claim 1 , wherein the controller is configured to provide one or more carrier gases for sample handling. 
     
     
       15. The apparatus of  claim 1 , wherein the controller is configured to provide one or more calibration gases to the sample preconcentrator. 
     
     
       16. The apparatus of  claim 1 , wherein the controller is configured to bypass a sample input to an exhaust line except during the adsorption mode, and is configured to provide the sample input to the sample preconcentrator during the adsorption mode. 
     
     
       17. The apparatus of  claim 1 , wherein a gas line connecting the sample preconcentrator to the gas analysis instrument is heated. 
     
     
       18. The apparatus of  claim 1 , wherein the controller provides a pressurized sample inlet. 
     
     
       19. A method for performing gas analysis, the method comprising:
 performing optical absorption spectroscopy with a gas analysis instrument, wherein the gas analysis instrument performs a spectral scan in a scan time T s ; 
 collecting an input sample gas with a sample preconcentrator having an adsorption mode and a desorption mode; 
 wherein the adsorption mode includes receiving the input gas sample and adsorbing one or more constituents of the input gas sample to collect one or more adsorbed species; 
 wherein the desorption mode includes heating the sample preconcentrator to release at least some of the one or more adsorbed species to provide a preprocessed gas sample; 
 switching between the adsorption mode and desorption mode of the sample preconcentrator with a controller; 
 wherein the preprocessed gas sample is provided to the gas analysis instrument in a desorption time T d ; 
 wherein T d  is at least 2T s . 
 
     
     
       20. The method of  claim 19 , further comprising controlling a temperature ramp rate of the desorption mode to control the desorption time T d . 
     
     
       21. The method of  claim 19 , further comprising providing enhanced concentration of an analyte species to the gas analysis instrument with the sample preconcentrator. 
     
     
       22. The method of  claim 19 , further comprising reducing concentrations of one or more interfering gas species provided to the gas analysis instrument using the sample preconcentrator. 
     
     
       23. The method of  claim 19 , wherein the optical absorption spectroscopy is selected from the group consisting of: cavity enhanced absorption spectroscopy, optical-feedback cavity enhanced absorption spectroscopy, cavity ring-down spectroscopy, tunable diode laser absorption spectroscopy, integrated cavity output spectroscopy, and off-axis integrated cavity output spectroscopy. 
     
     
       24. The method of  claim 19 , wherein the sample preconcentrator includes an adsorption/desorption medium selected from the group consisting of: porous polymers, graphitized carbons and carbon molecular sieves. 
     
     
       25. The method of  claim 19 , further comprising cooling part or all of the sample preconcentrator to a sub-ambient temperature during the adsorption mode to enhance adsorption of the one or more adsorbed species. 
     
     
       26. The method of  claim 19 , wherein the input sample gas is measured during the adsorption mode with the gas analysis instrument. 
     
     
       27. The method of  claim 19 , further comprising providing gas from the sample preconcentrator to one or more additional gas detectors. 
     
     
       28. The method of  claim 19 , further comprising performing one or more further sample preconditioning operations selected from the group consisting of: ozone removal, humidity removal, and selective removal of one or more interfering species with gas-selective membranes. 
     
     
       29. The method of  claim 19 , further comprising collecting one or more additional gas samples with one or more additional sample preconcentrators, wherein the controller is configured to connect an input of the gas analysis instrument to the sample preconcentrator or to any of the one or more additional sample preconcentrators, thereby providing multiplexing. 
     
     
       30. The method of  claim 19 , further comprising measuring one or more gas flows. 
     
     
       31. The method of  claim 19 , wherein one or more fixed gas flow restrictions is present to provide gas flow control. 
     
     
       32. The method of  claim 19 , further comprising providing one or more carrier gases for sample handling. 
     
     
       33. The method of  claim 19 , further comprising providing one or more calibration gases to the sample preconcentrator. 
     
     
       34. The method of  claim 19 , further comprising:
 bypassing a sample input to an exhaust line except during the adsorption mode; and 
 providing the sample input to the sample preconcentrator during the adsorption mode. 
 
     
     
       35. The method of  claim 19 , further comprising heating a gas line connecting the sample preconcentrator to the gas analysis instrument. 
     
     
       36. The method of  claim 19 , further comprising pressurizing a sample inlet.